(a) Field of the Invention
The present invention relates to a method and a system for enabling handover in a mobile communication network. More particularly, the present invention relates to a method and system for providing handover of a plurality of subscriber stations that have the same moving path.
(b) Description of the Related Art
A wireless portable Internet system such as a wireless broadband (WiBro) system or a high-speed portable internet (HPi) system is a type of mobile communication system. Such a wireless portable Internet system is a next generation communication scheme that provides mobility in local area data communication using a fixed access point (AP) such as a conventional wireless LAN.
Typically, in a wireless portable Internet system, a handover is a function that provides mobility of a subscriber station. Location and situation where the handover occurs differ for respective subscriber stations, and quality of service (QoS) also differs depending on a service mobile communication network that is used. Accordingly, an entire handover is processed between each subscriber station and a serving base station in a one-to-one correspondence.
Therefore, the wireless portable Internet system remains in an active state of services longer than a voice-dominated service system, and it performs handover more frequently than the same. For example, when a plurality of users are using the wireless portable Internet service in a transportation means such as a bus or a train, scanning as a pre-process of the handover and signaling as an actual operation of the handover are required to occur at respective terminals of the users at the same time.
FIG. 1 is a flowchart showing a conventional handover process of a plurality of subscriber stations.
Referring to FIG. 1, a plurality of subscriber stations collect cell information of a neighboring base station by receiving a neighbor advertisement (NBR-ADV) message from a serving base station (S110).
Subsequently, for a handover operation, each of the plurality of subscriber stations periodically performs a scanning process for checking a wireless state of a cell of the neighboring base station (S120).
When the subscriber stations move in the same direction and a handover condition for them is thereby satisfied, each of the subscriber stations requests handover by sending an MS-HO-REQ message to the serving base station. Then, the serving base station that has received the handover request separately sends a BS-HO-RSP message to each of the subscriber stations as a response to the handover request (S130).
Having received the BS-HO-RSP message from a serving base station, each of the subscriber stations separately sends an MS-HO-IND message to the serving base station to notify of handover completion (S140), and then performs a process for ending a connection with the serving base station (S150).
Subsequently, the subscriber stations start a ranging process with a target base station of a cell to which the subscribe stations has moved, and thereby sets up a connection thereto so as to receive a wireless portable Internet service (S160).
As describe above, when a plurality of subscriber stations escape from a cell of a serving base station and move to another cell of a target base station, each of the subscriber stations separately requests handover to the serving base station and performs a ranging process with the target base station of the cell to which the subscriber stations are moving.
When a plurality of subscriber stations simultaneously perform handover while moving together in a transportation means such as a train or a bus, transmission of messages for handover operation between the subscriber station and the serving base station abruptly increases so as to possibly cause insufficiency of a wireless band.
During a random access of the subscriber stations to the base station in order to request a resource allocation, probability of collisions with subscriber stations that are already handled by the target base station increases. In this case, latency increases.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.